Adaptive Beamforming Applied to Coherent MIMO Radar-over-Fiber Systems

In this paper, adaptive beamforming (ABF) techniques are applied to a coherent multiple-input multiple-output (MIMO) radar-over-fiber (RaoF) network for precise target localization. In the proposed system, a common central unit transmits and receives radio-frequency signals through optical standard single-mode fiber (SSMF) links, to/from remoted radar transmitters and receivers placed along a linear baseline. Electro-optical conversion is achieved through direct modulation of low-cost, power-effective, and high-speed vertical-cavity surface-emittina lasers (VCSELs). Among the available MIMO-ABF techniques, both data-independent and data-dependent approaches are taken into account. In particular, one estimation technique per family is analyzed (i.e., data-independent, data-dependent without array steering vector errors and data-dependent with array steering vector errors), i.e., respectively the least-squares estimator, the Capon and the robust Capon beamforming techniques. The advantages and disadvantages of these techniques are illustrated through their application to experimental X-band data acquired with a MIMO RaoF system in a controlled scenario.